Signaling system



June 25, '1935. M ALMQUlsT ET AL SIGNALING SYSTEM Filed Aug. 29. 1953 2 Sheets-Sheel 1 June 25, 1935. M, L, ALMQulsT ET AL 2,005,836

SIGNALING SYSTEM Filed Aug. 29, 1955 2 sheets-sheet 2 Patented June 25, 1935 UNITED vSTATES PATENT OFFICE ySIGrNALINGr SYSTEM Milton L. Almquist, Maplewood, N. J .,and Albert C. Thompson, New York, N. Y., assignors to American Telephone and Telegraph Company,

a corporation of New Application August 29,

4 Claims.

l mit signaling operations to be carried on regardless of whether the circuit is in use for speech transmission or not. These channels have the additional advantage that they may be operated on what may be termed a continuous basis as compared with channels which are operated on `a spurt basis, that is, their operation is such that a signaling device maybe operated at the -distant end of a circuit kby the application of signaling current at the local end and this signal will be held operated as long as the signaling current is applied and will be released when the signaling current is removed. In the spurt system the signal at the distant point is operated by a spurt of signaling current sent over the line and the signal is locked in by auxiliary control arrangements and released by another spurt of signaling current sent over the line.

In the toll plant'it has not heretofore been practicable to obtain the advantages of direct current Aor other independent signaling channels except in certain special cases, due to the fact that the available direct current channels have generally been used for telegraph purposes and because the cost of other independent rchannels has ordinarily been prohibitive. Evenwhen direct current channels are available, their use for signaling purposes is limited, except for the shorter circuits, because of cost and performance considerations. It is the principal object of this invention to provide means for obtaining substantially the same results with voice-frequency signaling channels as are obtainable withdirect.

current or other independent signaling channels.

Other objects and features of the invention will appear more fully from the detailed description thereof hereinafter given, when read together with the accompanying drawings in Figures 1 and 2 of .which the invention is illustrated. Figs. 1 and 2 when placed side by side, with Fig. 1 on the left and Fig. 2.on the right, constitute a circuit diagram embodying a preferred form of the invention. l

In the Figs. l and. 2 of the drawings, when placed side by side, are 'shown two stations inter- Yorkl 1933, serial No. 687,368

(c1. 17a- 43) v connected by a toll line L. Voice-frequency signal receiving apparatus I and 6, both of twhich may be of the same type and well known in the art, and voice-frequency signal sending apparatus eonsistingof the generators Gx and Gy and the sending relays S and S are provided'at the stations of Fig. l and Fig. 2, respectively. In" additi-on, there are also included the cut-off relays vCO and CO which serve to open the talking circuits to the switchboards, the circuits of which are shown in the ngures for purposes of illustration. These relays prevent the signalingcurrentsv from reaching the subscribers. k In conjunction with the voice frequency lequipmentenumerated above, the signaling relay arrangements 2 and l are provided as part of the signaling apparatus at the stations of Figs. 1

and 2, respectively, and these arrangements serve to translate the signals passed over the line' L by the voice-frequency equipment in such 'a way that the action of the complete signaling channels from the Out signaling lead at one station, for example, lead lill of Fig. l, to the In signaling Alead at the other station, for example, lead mi of Fig. 2, is substantially the same as though the signals had been passed over direct current channels or other independent channels between the two stations. In order to'properly control the relays in these arrangements', it is necessary to include the" additional Out and In leads 03, H34, HB3 and |04 designated in the drawings as auxiliary control leads, which are employed for the control of the signaling relay apparatus 2 and 'l involved in the transmission of signals over the line L and over the signaling Out and In leads IUI, |02, |0I

and |02', as will be described hereinafter.

Before giving a detailed description of the operation of the` arrangements of the invention, the various functions that the signaling arrangements of the invention perform will be briefly described. These functions are as follows: When the operator at the station of Fig. 1 makes a connection with the telephone line extending to the station of Fig. 2, the signaling system will cause a signal lamp to light at the switchboard at the station of Fig. 2. The operator at the station of Fig. 2 will then answer and get instructions for the completion of the call from the operator at the station of Fig. 1, and when' the operator at the station of Fig. 2 establishes the connection to the toll switching .trunk to the' subscribers local office, the signal lamp at the stationfof Fig. 2 will go out. When the operator in the'subscribers local oiiice of Fig. 2 completes the connection to the called line, the signaling system on the toll line functions to cause a supervisory lamp at the station of Fig. 1 to light to indicate the progress of the call to the operator at that point and when the subscriber answers, the signaling f system causes this light to be extinguished. When the subscriber at the station of Fig. 2 hangs up his receiver on the completion of the call, the signaling system causes the lamp at the station of Fig. 1 to light again as a discon-` nect signal, and when the operator at the station-- of Fig. 1 takes down the connectionfthis lampv is extinguished and the signaling system causes the lamp at the station of Fig. 2 to light as a disconnect signal for the operator at the stationv of Fig. 2. When the operator at Fig. 2 disconnects, the lamp goes out and the circuit restores to normal. At the same .time a disconnect signal is also given to the operator in the subscribers local office at Fig. 2. The signals which Y. a; busy-back, jack, due to all the trunks being busy. or yto the called .subscribers Vcircuit being in use, orby the subscriber at Fig.. 2 actuating hisr switchhook in order to signal the operator at Fig. 1. They may also be caused by the operator at Fig.1 ringing the operator at Fig. 2. in order to recall her after she has cut out of the connection.

.L The ioperation of the arrangements of the in-V ventionwill now be described in detail. When the circuit is idle, voice-frequency signaling currents are transmitted'over the line `L in each direction. These currents .will preferably be of the formnow'used in telephone practice, that is, a voice-frequency carrier interrupted at a lowlfrequency rate, but they may be of other forms 1 if desired,.provided the'resulting signaling system hassubstantially the same characteristics as regards freedom from interference dueto speech currents, tones, noise, etc., as the present system. For purposes of illustration it will be assumed'that la current of 1400 cycles interrupted at a30 cycleirate will be transmitted from Fig. 1 to'Fig. 2 and a current of 1000 cycles interrupted atia 30 cycle rate Will bevtransmitted from Fig. 2 toFig. 1. The 1400-30 cycle current is supplied bythe source GX and is connected to the line throughthe contacts of relay S, which is held normally operated byground supplied over leads 4 and 33 and the contacts of relays D and E. Similarly, the 1000-30 cycle current from source Gy in Fig. 2 is connected to the llnethrough contacts of relay S', which is held normally operated by ground supplied over leads.9 and 21 and the contacts of relays D and E. The cut-off relay CO in Fig. 1 is held operated by ground supplied to lead 5 from either leada or lead 5b.. The ground on lead Salis `obtained through the contacts on relay S,A as'shown, While the ground on lead 5b obtainedl through the contactson relay-A, rlead 32'and the contacts on relayF. The

cut-off relay .COlin Fig.` 2 is valso held operated by ground similarlysupplied over leads In, Illa,

v III and 29,A and the contacts on relays S', A',

the toll line L from reaching the switchboards, and hence from the subscribers.

At the station of Fig. l, the incoming signaling currents pass over leads 36 to the receiving circuit I, where, after being amplified and detected by the vacuum tubes I I and I2, respectively, they cause the polar relay I3 to vibrate in accordance with the 30 cycle interruptions of the Asignaling current. The operation of relay I3 in conjunction with the tuned circuit I5 and relay I4 causes relay I4 to operate and remain operated steadily for the duration of the incoming signal in a manner well 'known in the art. The contacts of Aof circuit 2 operated, the effect of which will be explained subsequently in `connection with the ing circuit, .as previouslydescribed, but prevents'v the vMOO-cycley signaling voltage from reaching the tube andl operatingthe receiving circuit'.

yrelay I4 supply ground over lead 3 to hold relay f The receiving circuit 6 vof Fig. 2 is similar in manner similar to that described above for circuit I and causes'ground to be applied to lead 8.

From the above it will'be seen that as long as signaling current` is applied to the. line at Fig. 1, ground will be present on lead 8 in Fig. 2, and that as long as signaling current is supplied .to theline at Fig.. 2, ground will be present on lead 3 of FigQl. Removal ofthe signaling current at either end will accordingly cause an indication tobe given at the other end by the ground being removed from lead 3 or lead Slasthe case may be. Conversely, applying the signaling cur-` rent at either end will also produce an indication at the distant end by causing the application of ground to lead 3 or lead 8, as the case may be. 'I'hese voice frequency channels are controlled by the relay circuits 2 and 'I of Figs. 1 and 2, respectively, in a manner which is hereinafter described.

When a'call is originated by theoperator at the station of Fig. 1, ground will be placed on the Out signaling lead IUI and the Out auxiliary. control lead ID3 by the switchboard circuit of Fig. 1 in a manner to be hereinafter described.y

ground applied to lead 4 through'the back con tact of said relay, lead 33, and the back contact of relay D. This makes relay S release and re-` move the 1400-30 cycle current from the line by opening the connections to the generator GX. The release of relay S also removes ground from the cut-off relay CO over leads 5a and, 'but this 'does not cause the release of relay CO. since ground is still applied to it from relay A through 'Y interrupted ground on lead i132.

lead 32, the back contact of relay. F, and leads Saand 5. f

Theremoval of the 1400-30 cycle signaling current fromk the line causes the signal receiving circuit or Fig. 2 to remove ground from lead 8, as hereinbefore described. This causes the release of relay A' which connects ground through lead 24 and the back contact of relay'B to the In signaling lead' I02. This ground causes a signal to be brought in at the switchboard of Fig. 2 by means hereinafter described. It will thus be seen that grounding the Out ysignaling lead IBI of Fig. 1 will cause ground to be applied to the In signaling lead |02 of Fig. 2. It will be evident later from the description of the disconnect signals that removing the ground lfrom lead IIJI will cause the groundv to beremoved from lead E62', so that the action of the signaling channel from the Out signaling lead of Fig. l to the In signaling lead of Fig. 2 is therefore essentially the same as it would be if a direct current or other independent signaling channel were used between these leads. Obviously an interrupted ground on lead IIli will produce an When relay A is released, ground is also applied to the lower terminal of the winding of relay C over lead 25, thus operating relay C. In addition, the ground being applied through lead 2S, the back contact of relay F and over leads les and Ill to the winding of the cut-oil relay CO', is removed. Relay CO does not release at this time, however, since it is still supplied with ground from relay S' over leads Illa and it?. The operation oi relay C' connects ground to the winding of relay F over lead 28, thus operating relay F. Relay F transfers lead 29 from itsV connection with lead Ib to a connection with lead 3l and the winding ofrelay G, thus preparing a path for operating relay G when relay A' ren operates.

The ground on the Out auxiliary control lead I3 of Fig. 1 causes the operation of relay B, which prepares a locking path for itself over lead I'I, transfers the In signaling lead I2 from its connection with lead 26 to a connection with lead I8 in preparation for the reception of supervisory signals which will be transmitted from Fig. 2 in a manner to be hereinafter described, and connects ground to lead I9 tofprepare a locking circuit for relay C. l a

When the operator at the station of Fig. 2answers, the switchboard circuit causes ground to be placed on the In auxiliary control lead |04', which groundcauses relay D to operateand ren move the ground it was applying over lead 2l to lead 9 and the winding of relay S. This causes relay S' to release and remove the 100G-30 cycle current from the line by disconnecting the` source Gy. With relay S' released, ground is no longer supplied to relay CO over lead Illa and I0, and since ground has already been removedy from lead Ib, as previously described, relay CO releases and connects the line through to the switchboard. Relay D, in addition to its above mentioned function, provides ay holding path for relay F by applying ground to lead 28. n

The removal of the 100G-30 cycle current from the line causes the voice-frequency receiving circuit I of Fig. 1 to remove ground from lead 3, as hereinbefore described. This causes relay A to release and apply ground overlead 2 I to the winding of relay C, which operates and locks up over lead I9 to ground supplied through a front contact on relay B, while relay B locks up to ground supplied over lead I'I from a back contact 'of re- I lay A. This locking up of relay C through the contacts of relay B is required to prevent relay C from releasing when relay A is subsequently operated and released, as hereinafter explained, .in

connection with the ltransmission of supervisory Y signals from Fig. 2 to Fig. 1. The locking path for relay B is necessary to prevent a false signal being given to the inward operator at Fig. 1 in case the outward operator at that point should disconnect, through error, while the subscribers are talking, The operation of the rcircuit under the latter condition is somewhat different from its normal action and is described in detail hereinafter. The release of relay A also removes ground from leads 32, t and 5, thus releasing relay CO and connecting the line through to the switchboard. The circuit is now in the talking condition and the operators may communicate with each other over line L. The operation of relay C applies ground over lead 23 to relay F which operates and transfers lead 32 from its connection with lead 5b to a connection with the winding of relay- G over lead 2U, thus preparing a path for operating relay G upon the reoperaton of relay A. Relay C also prepares a path for bringing in the supervisory signal in the switchboard of Fig.v

ception of the supervisory signals which will be. transmitted from Fig. 2'to Fig. l in order that the A'. operator at Fig. l may follow the progress of ther 40 When the operator at the station of Fig. 2 has call. These signalsfare sent as follows:

ascertained the called number from the operator at the station of Fig. l, she passes the required in-y formation over a toll switching trunk to an operator in a local cnice, as will be hereinafter eriM i;

from the source Gy. Mlay S also connects ground to relay CO over leads Illa and II), causing relay v CO' to operate andopen the connection between the line L and the switchboard. 4

With the 1099-30 cycle current on the line, the voice-frequency receiving circuit I of Fig. l operates as hereinbefore described and places ground on lead 3. Ground on this lead lcausesrelay A to operate and apply ground over lead 22, one of the front contacts of relay C, lead I8 and one of the front contacts of relay B to the In signaling lead |62. Ground on lead m2 causes the supervisory lamp inthe switchboard cord circuit to light, ina manner to be hereinafter described. Relay A alsosupplies ground over lead 32, the front contact of relay F, and lead 22 to the wind,- ing of relay G, which operates Vand connects ground over leads 5b and 5 to the cut-off relay CO.

lease characteristic of relay G.

This causes relay CO to'operate. and disconnect the line from the switchboard.

When the called subscriber answers by removing his receiver from the switchhook, the switchboard circuitv at Fig. 2, in a mannerv to be hereinafter described, removes the ground it was supplying to the out lead I I at that point. With ground removed from lead |0|', relay E releases and removes the ground being supplied to relay S over leads 30 and 9, thus causing relay S? to release and remove the 1000-30 cycle current from the line. When relay S releases, it, also removes the ground it was supplying to relay CO -over leads |03 and I0, and relay CO releases and reconnects the line to the switchboard.

The removal ofthe 1000-30 cycle current from the line causes ground to be removed from lead 3 of Fig. 1, `as previously described. This causes relay A to release and remove the ground it was supplying over leads 22 and IB and contacts on relays B and C to the "In signaling lead |02. Removing ground from lead |02 causes the supervisory lamp at the switchboard at Fig. 1 to be extinguished, as will be hereinafter explained. The release of relay A also removes the ground being applied over leads 32 and 20 and the front contacts of relay -F to the windingA of relay G, which releases. When relay G releases, it revmoves the ground being applied over leads b and 5 to the Winding of relay CO, which releases and reconnects the line to the switchboard. There is a short delay between the release of relay A yand the release of relay CO due to the slow re- This delay serves no useful purpose at this time, but has been provided to improve the operation of the system when intermittent signals are transmitted in the manner to be hereinafter explained. The circuit'is now in the talking condition again and ready for the subscribers to carry on their conversation.

From the above description it may be seen that with certain relays operated in' circuits 2 and 'I pendent channel; that is, grounding lead |0| causes ground to be applied to lead I 02 of Fig. 1 and removing the ground from lead |0| causes ground to be removed from lead |02. Obviously, if an intermittent ground is applied to the Out signaling leadv |0|.` of Fig. 2, as may occur if either of the operators at the station of Fig. 2

Y makes a connection to a busy-back jack or if the subscriber operates his switchhook in order to signal the operator at Fig. 1, an intermittent ground will be placed on the In signaling lead |02 of Fig. 1.

It may be noted in connection 'with these intermittent signals that as far as the application of the sginals to the line L at Fig. 2 vand their reception at Fig. l are concerned, the same result will be obtained if an intermittent ground is placed on lead |04 while a steady ground is present on lead I0 I Also, if an intermittent ground is applied toeither lead IOI or |04 without a steady ground on the other, an intermittent ground will be applied to lead. |02 of Fig. 1, but this ground on lead I 02 will be reversed in phase from that on leads |0| or I04',`that is when the ground is applied to lead |04', the ground on lead v|02 will be removed, and when the ground is removed from lead |04', it will be applied to lead |02. 'I'he condition of an intermittent ground on lead |04 Without ground being present on lead |0| may occur in case the operator at Fig. 2

should desire to ash the operator at Fig. 1 in case of a cut-off at Fig. 2, as hereinafter described. y

In connection with the operation of the system on intermittent signals it should also be noted that there is a short time lag between the application of the voice-frequency signals tothe receiving circuit l andthe subsequent operation of relay A and the cut-off relay CO, during which time interval, a. short spurt of voice-frequency current is being transmitted .to the switchboard and hence to the subscriber. This momentary spurt of voice-frequency current is of no particular consequence when steady signals are involved as it only occurs once, butit would be objectionable to-have it occur with every impulse when intermittent signals are involved. In order to obviate this condition, theslow-release relay G has been included in the circuit. When relay A operates intermittently in accordance with the intermittent signals beeing transmitted over the line, it applies ground intermittently to the In signaling lead |02 and to relay G. If relay G were of the fast functioning type it would follow the interruptions and cause relay CO to pulse, with the result tha'tspurts of the 1000-30 cycle current would be transmitted to the switchboard as indicated above; but by making relay G sufliciently slow-release to hold over the interruptions, ground is helden the leads 5b and 5 until the conclusion of the intermittent signals and thus relay CO is kept operated during the time the intermittent signals are on the line.V

At the conclusion of the call, both parties hang up, and when the called party at Fig. 2 does so, steady ground is placed on the Out signaling lead I0 I This causes ground to be connected to the In signaling lead |02 at` Fig. 1 as hereinbefore described and the supervisory lamp L2 in f the switchboard at Fig. 1 lights steadily as a disconnect signal. The operator at Fig. 1 then pulls down the connection and the switchboard circuit removesground from the Out signaling lead |0| and the Out auxiliary control lead |03. With ground removedfrom lead |0|, relay E releases and reconnects ground through its back contacts, lead 33, and the back contacts of relay D to lead 4 and the winding of relay S. Relay S reoperates and reconnects the 1400-30 cycle current to the line. It also supplies ground over leads 5 and 5a `to the winding of relay CO which is alreadyoperated by ground-from relayy G over leads 5b and 5. y f

Immediately upon the removal of. ground from lead |03, relay B releases since its holding path over lead II isv open at the' contacts of relay A, which is operated. `When relay B releases, it removes the` ground being supplied'tothe In signaling lead |02v over leads I8 and 22 and the contacts of relays A and C, andalso removes the ground being furnished to relay C over lead I9. This releases relay C Whichopens its locking path to lead I9, opens the connection between leads I8 and 22, and removes ground from lead 23. Removing the ground from lead 23 causes relay F to release andopen the connection between leads 32 and 20, which inA turn causes relay G to release. At the same time relay F establishes a connection between leads 32 and 5b, over which ground from relay A is now transmitted to lead 5 and the Winding of relay CO. This has noA efby its slow releasev characteristic, it removes the" ground being supplied through its contacts to lead 5t, which removal also has no effect at this time. Circuit'2 has now restored to its original condition.

-In Fig. 2, the restoration of the 1400-30 cycle current to the line causes-ground to be applied to lead S. reoperates relay A.' which re moves the ground being supplied through its contacts to lead 24 and thence through back con tactson relay B' to the fIn signaling lead |02. Removing the ground from lead |02' causes lamp L1' at the switchboard at Fig. 2 to light as ay disconnect signal, in a manner to be hereinafter explained'A When relay A operates it also applies ground over lead 29, the armature and front contact of relay F' and lead 3| to the winding of relay G', which operates and applies ground to. lead mb and thence via lead I0 to relay CO is already operated by ground supplied over leads ma and Hl from relay S", which is operated. In addition, relay A' removes the ground being applied to relay C over lead 25, thus causing relay C' to release. On releasing, relay C' removes the ground it was supplying to the winding of relay F' over lead 23, but relay F' does not release because it is held operated by ground applied to lead 28 through the contacts of relay D', which is still operated.

` v When the operator at Fig. 2 takes down the connection in response to the disconnect signal received from Fig. l as indicated ab`ove,ground will be removed from the Out signaling leadv ,lead 9, instead of over their front contacts and lead 30, and relay S' accordingly remains operated. When relay D releases, itV also removes ground from lead 28 and the winding of relay F', thus permitting relay F' to release. With relay F' released', the ground being supplied from relay A over leads 29 and 3| to the winding of relay G is transferred to lead |81). thereupon releases and removes the ground it was supplying to lead |01). Circuit 1 hasnow re- In oase the operator at the station of Fig. 1 should for any reason Wish to recall the operator at the station of Fig. 2 (before having dis'- connected, of course), she may do so by operating afringing key (not shown) in her cord cir- `of Fig. 1 will be'repeated on lead |52' of Fig. 2,

so that an interrupted groundwill be placed on lead m2', which interrupted ground will cause the inward operators lamp Li to flash at Fig. 2, by means hereinafter described. The intermittent ground on lead |02' is caused by the intermittent operation of relay A' in' accordancev with the intermittent voice-frequency signals received over the line. Relay C' follows the` pulsationsofgree 'lay A', but relay F does' not do sov inasmuchas itis held operated by ground over lead 28 fromy the contacts of relay D. Relay G', whiclrisof the slow-release type, serves tokeep the cut-off relay CO operated steadily during the intermit,

tent signals in the same manner as relay G per'.- forms the same function .at Fig. l, as hereinbe. fore described. f f

As hereinbefore indicated, the operation ofthe circuit is somewhat different in case the operator at Fig. 1 should erroneously take down the connection before the subscribers were thro-ughtalking. When this occurs, the disconnect.' signals will be transmitted as follows: With the circuit in the talking condition relays B, C and Fare operated at Fig. l and relays D', C'y `and F' are' operated Aor at Fig. 2. When the operator takes down the;

connection, ground-will be removed from `the Out signaling lead itil andthe Out auxiliary` control lead H33, as in the normal case. With ground removed from lead l!) relay E will release' and connect ground through its back conta'ctsandV also supplies'ground over leads 5 and'5a to relay' CO which operates kand disconnects the switchy board from the line.. ylf'telay B does not release at this time, however, even. though ground has been removed from lead |03, inasmuch'as it is locked up over the circuit through its contacts,lead

and the contacts of relay A to ground.. 'This locking up of relay B is necessary.` in order topre- Vent ground from contacts* on relay A passing' over lead 26 and the contacts of .relayBto lead |02, which ground would cause a false signal to .i be brought in before the inwardoperator atthe station of Fig. 1. At Fig. 2, the restoration or the 1400?-30 cycle current to the line causes ground to be applied to lead 8. This operates relay A which removes the ground being supplied through its contacts to lead 24 and thence through back contacts on relay B to the In signaling'lead |02'. Removing` this ground from lead |22 causes the lamp L1' to light as: a' disconnect signal at the switchboardof Fig. 2. When relay A" operates' it also causes theoperation of relays G' and CO' and the release of'rel'ay'C' in the same manner as for a normal disconnect, `as hereinbefore described.

When the operator at station ofFigg'2'disconnects in response to the signal, ground will bei removed from the In control lead |04 by the` operation of the apparatus .in' the switchboard circuit. lThis. releases relay D', which applies gro-und from its back contacts over lead 2l, the

contacts of relay E which is released in the' pres-fent case, and lead 9 to the winding of` relay S',

which operates and connects the 100G-30 'cycle current to the line. Relay S' suppliesv ground through its contacts to lead Ita and thence via lead it to relay CO',l but this serves no useful purposev at this time since relay CO is already operated. When relay D releases, it also' removes thel 'ground which was being supplied over leadv 28" to the winding of relay,F, which releases 'and'k transfers lead 29r from its connection withleadll groundl to be applied/to' lead 3,' whichfg'round causes relay A to operate. Theoperationbf re-` lay A removes thegroundbeing'applied over lead@ Il' and thev contactsof relayfB to the winding or i relay B; thus permitting" relayB 'to release. At

the same time relay A removes the ground it was' The release of relay B opens the holding circuit for relay C which then releases and removes ground from the winding of relay F, which also releases. When relay` F releases, it permits relay G to rey lease, as hereinbefore described, and the circuit l5- becomes restored to normal without `causing a false signal.

In case the operator at the station of Fig. 2 should'pull down the connection before the subscribers have hung up, the ground being supplied from the switchboard circuit to the winding of relay D over lead |04' will be removed and relay l D' will release.

This causes the operationof relays S' and CO' in a manner hereinbefore described, and'1000-30 cycle current will be applied to the line L. At the same time ground from the contacts of relayY A' kis still being supplied over leads 24 and |02' to the switchboard circuit, and

, with the inward cord down, this ground causes the lamp L1I` associated with the cord to light, in a manner tobe hereinafter described, thus calling the attention of the operator at the station of Fig. 2 tothe fact Vthatshe has broken the'connection. i i 1 At the station of Fig. 1, the 1000-30 cyclecurrent'causes the operation of relay A, which applies ground over leads 22, I8, and |02 to the switchboard circuit, in a manner previously described, thus causing the supervisory lamp L2 to light.` Since the calling subscriber has not hung up, the operator at the station of Fig. 1 also knows that there has been a cut-off. If the operator at the station of Fig. 2 knows the called numberV and reestablishes kthe connection, relay D' at Fig. 2 will be' reoperated, the lamp L1' at Fig. 2 will be extinguished, the signaling current will be removed from the line L, the relays at Fig. 1 will re-` store to the condition they normally assume during the talking interval, and the supervisory lamp Lz at Fig. 1 will be extinguished. If, however, the operator at the station of Fig. 2 does .not know the called number, she may flash the operator at Fig. 1 by operatingV her talking key K' several times, which will operate relay D' intermittently. This will apply the signaling current to the line L intermittently and cause the lamp L2 at Fig. 1 to flash as hereinbefore described. When the operator at the station of Fig.` 1 answers, the operator at the station of Fig. 2 may ascertain the vcalled number and reestablish the connection Yas above.

VA detailed description has heretofore been given of the operation of the arrangements of f the invention in Figs. 1 and 2 for the various types of signals applied to the incoming and outgoing signaling and auxiliary control leads. A description" will nowbe given of the operation of the switchboard apparatus of Figs. 1 and 2 to illustrate how these various signals are applied to and from the outgoing and incoming signal and auxiliary control leads.

In Fig. 1 is shown the switchboard apparatus associatedwith one` end of the signaling system, consisting of the apparatus associated with the toll line L, an operators cord circuit, and the toll ofl'icel end of a toll switching trunk. Similar switchboard apparatus for the other end of the system is shown in Fig. 2.

When an operator at the station of Fig. 1 receives word that a connection is desired with the toll line, she will insert the plug P1 of her cord in the jack J1. This will operate relay S1, which in turn will operate relay A1. The operation of relay A1 sets the busy signals BS and places ground on the Out signaling lead |.0 The application of this continued ground to lead |0| will, through the arrangements of the invention, cause ground to be placed on the In" signaling lead |02' of Fig. 2, in a manner hereinbefore described in detail. The contacts of relay. S1 also place ground upon the Outv auxiliary control lead |03, which ground serves to condition the signaling apparatus 2 of. Fig. 1 for the reception of signals from the station of Fig. 2, as previously described.

To reach the calling subscriber, the operator at the station of Fig. 1 inserts plug P2 of the cord in jack J2 of a toll switching trunk and passes'the number to the operator in the local oflice, who

establishes the connection. When the subscribers line is connected to the trunk, relay G1 will operate and connect the upper winding of relay S5 in parallel with its lower winding, thus lowering the sleeve resistance to a predetermined value and causing the lamp L1 associated with the trunk end of the cord to light. When the subscriber answers relay G1 will release, the sleeve resistance will change back to a higher predetermined value and the lamp La will be extinguished. Obviously, if the subscriber operates his switchhook, the lampv L3 will flash, and when he hangs up the receiver at the conclusion of the call, the lamp L3 will light steadily.

The application of ground to the "In signaling lead |02' will cause the operation of relay C1' of- Fig. 2. This causes the busy signals BS' associated with the line L to be operated and also lights the incoming signal lamp L1. The operator at the station of Fig. 2, upon thelighting of lamp L1', will operate her talking key K' and receive the necessary information regarding the call from the operator' at thestation of Fig. 1 (by means fof a telephone set not shown), and Will' then insert the inward plug P3' into the jack J2' of a toll switching vtrunk at Fig. 2 and pass the In auxiliarycontrol lead |04' in order to keep ground-on this lead after the talking key K' is released, and operates relay B1', which extinguishes the lamp L1' and provides a holding circuit for vthe busy signals BS' to take the place of the one supplied by relay C1' which now releases. In addition, relay B1 applies battery through its contacts to the armature of relay D1' and transfers the In signaling lead |02' to the winding of relay D1', which operates since there is ground on lead |02'. l I

When the operator in the local office at the station of Fig. 2 establishes the connection to the subscribers line, relay G1 in the toll switching trunk operates and lowers the resistance of the ground is applied to the In signaling lead H32,

relay S2 willbe operated. The operationof relay S2 connects a resistance in `shunt with the .I winding of relay S1 and thus reduces the `sleeve resistance of vjack J1 to a lower predetermined value, which causes the lamp L2 associated4 with the toll end fof the outward cord circuit to light. Thus, when a connection is established with the subscribers line at the station of Fig. 2, the lamp L2 at Fig. i will light.

When the subscriber at the station of Fig. 2 answers, relays. G1' and S4 at Fig. 2 release. This will remove ground from lead il. at Fig. 2

-, and remove ground from lead |02 at Fig. l and mittent ground is applied to lead Ii' by thebusy signal circuits at Fig. 2, the lamp L2 at Fig. 1 will flash.

When the subscriber at the station of Fig. 2 hangs up, relays G1 and Si' reoperate and the lamp L2 at Fig. 1 will light steadily. If the sub scriber at the stationl of Fig. 1 has also hung up, the lamp L3 associated with the trunk end of the cord circuit will also lighty as hereinbefore described. Both lamps being lighted indicate to the operator at the station of Fig. 1 that she should disconnect, which she does by removing plugs P1 and P2 from the jacks J1 and J2 of the toll line L and the switching trunk, respectively. Removing the plug P1 from the line jack J1, eX- tinguishes lamp L2 and causes relay S1 to release, which in turn releases relay A1 and also removes ground from llead iBS. The release of relay A1 removes ground from lead lili, releases the busy signals BS, and transfers lead i2 from its connection to the winding of relay S2 to a connection with the winding of relay C1 through the contacts of relay B1. Relay S2 releases, but relay C1 does not operate at this time because the removal oi ground from leads lill and |03 4has caused the ground on lead IGZ to be removed, as hereinbefore explained. Removing the plug P2 from the switching trunk jack J 2 causes the lamp L3 associated with the trunk end of the cord to go out and releases relays G1 and S5 in the trunk, the release of which relayscauses a disconnect signal to appear at the local cnice.

The removal of ground from leads lill and 103 causes the signaling system to send a signal over the line by the arrangements of the invention and restore itself to normal, as previously described. This signal causes ground to be removed from lead m2 at Fig. 2 and causes relay D1 at Fig. 2 to release and supply battery to light lamp L1 which will light asa disconnect signal for the operator at the station of Fig. 2. When the operator at the station of Fig. 2 responds to the disconnect signal and removes the plug P3 from the jack J 2 of the switching trunk,

relays S3 and S1 in the toll line circuit and relays G1 and S5 in the trunk release. With relay S2 normal, relay B1 releases and deenergizes the busy signals BSr and removes the bat-v tery being supplied through the contacts `of relay D1 to the lamp L1', which goes out. When relay S3' releases, it alsoremoves ground from lead |64', while the release of relay Si removes ground from lead ll. The removal of ground from these leads causes relay circuit 'I `to restore to normal as hereinbefore described. The release of relays S5' and G1 in the switchingtrunk causes a disconnect signal to be given to the operator in. they local oflice. the local offices at the stations of both Fig. V1 and Fig. 2, havexdisconnected, the entire circuit will be in its normal condition.

If the outward operatorat the station of Fig.

1 wishes to recall the operator Aat the station of Fig. 2, she does so 'by operating the ringing'key (not shown) in the outward cord circuit. This key applies battery through the .tip of plug P1 to the tip of the line and thence to the winding of relay K1, which operates. Relay K1 removes the steady ground being supplied to lead lili from relay A1 and replaces this steady ground by an intermittent ground. This causes the steady ground on lead m2 at Fig. 2 to change to an intermittent ground in a manner hereinbefore described. With relay B1 at station Y operated, y

as it is when a recallsignal is being transmitted, this intermittent ground on lead |02 causes re'- lay D1 to operate intermittently and ash lamp.

104'. This will cause a signal to be transmitted to Fig. l, which signal will cause the supervisory-` lamp L2 at Fig. 1 to light, ras hereinbefore de scribed. When relay S3 releases, it also releases relay B1', whichtransters lead E02 from the winding of relay D1 to the winding of relay C1. rIhis causes relay D1 to release, andk since ground is present on lead 02', relay C1 operates and causes lamp L1 t-o light. In addition, relay C1 also holds the busy signals BS operated.

The lighting of lamp L1 when the cord is down is an indication to the-,operator at the station of Fig. 2 that .she has broken the circuit. If she can kreestablish the connection immediately, relay S3 will be reoperated and will in turn reoperate relay B1 and apply ground to lead 104. tinguished, relay D1 will be reoperated, and relay C1 will release and extinguish lamp L1" and the circuit will be in the talking condition again.

The lamp L2 at Fig. l will be exl l0 When the operators in If, however, the operator at the station of Fig.

2 Vdoes not know the called number, she may flash the operator at the station of Fig. 1 and obtain it from her, after which she can reestablish the connection as just indicated. Inasmuch as the inward cord is down so that relay S3 is released, the operator at the station of Fig. 2 may flash the operator at the station of Fig. 1 by operating her talking key intermittently. This will cause an intermittent ground to be placed on lead |04', which will cause intermittent signals to be sent over the line L, and as hereinbefore indicated, such intermittent signals will cause the lamp L2 at Fig. 1 to ilash.

Although the invention has been described on the basis of calls being originated at the station of Fig. 1 and received at the station of Fig. 2,

4the circuits are entirely symmetrical and may be operated just as readily for calls' going in the reverse direction.

, While the invention has been disclosed in certain specic arrangements'which yare deemed desirable, it is understood that it is capable of embodiment in many and other Widely varied forms without departing from the spirit and scope of the invention as defined by the appended claims. What is claimed is:

1. The method of signaling over a telephone circuit which consists in transmitting from one end of said circuit while said circuit is not in use for the transmission of telephone currents, van alternating current of a first frequency, transmitting from the other end of said circuit while said circuit is not in use for the transmission of telephone currents, an alternating current of a second frequency, removing the current of the `iirst frequency from the telephone circuit so that an indication is provided at the distant end When a telephone connection isl desired, removing the alternating current of the second frequency to clear the circuit for the telephone connection, reapplying and subse-- quently removing the .alternating current of the second frequency to said circuit at the distant end, indicating at the rst end of said circuit the application and removal of said alternatingk current, and reapplying the alternating current of the rst frequency when the circuit is to be restored to its original condition.

2. The combination of a signaling circuit which is capable of transmitting speech currents as well as auxiliary signals, means for'simultane-- ouslytransmitting auxiliary signals in opposite directions over said signaling circuit While said circuit is not transmitting speech currents, means for removing the auxiliary signaling current transmitted over said signaling-circuit in one direction when connection is made to the signaling circuit for the transmission of speech abonn currents, means responsive. to removal of the latter auxiliaryl signaling circuit for indicating at the opposite end of the circuit that a con-v nection is for the transmission of speech currents to be made to said circuit, and means for removing the auxiliary signaling current trans mitted over the signaling 'circuit in the reverse direction when said connection is, made. 3. The combination of a circuit which is capable of transmitting yboth speech currents and auxiliary signaling currents, means for simul-v taneously transmitting alternating currentusignals vof predetermined frequencies in oppositev directionsV over said circuity as auxiliary signaling currents for said circuit while said circuit is not in use for the transmission of speech currents, means `for removing said auxiliary signaling currents from said circuit, means'for subsequentlyy reapplying said rauxiliary signaling currents to said circuit, andmeans responsive to the removal and reapplication of said lauxiliary signaling currents to provide calling and supervisory indications of the condition of said circuit.

4. The combination of a circuit which is capable of transmitting both speech currents and auxiliary alternating currents, means for simultaneouslyk transmitting said auxiliary alternating currents in opposite directions .over said circuit While said circuit is not in use for the transmission of speech currents, `means for controlling the application andrremoval of said auxiliary ,alternating currents, a plurality of calling and supervisory signals for indicating the condition of said circuit and meanspresponsive to the removal `and reapplication of said auxiliary alternating currents for operating said calling and supervisory signals. 

